Heat Pumps vs Gas Pipelines

Arlington

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I believe Mass has made the right choice to promote heat pumps (as a way of reducing natural gas usage)

A quick doodle;

Gas heat can never be more than 100% efficient. Burn 1 btu, get a Btu into your living space. Burn a KWh, get a KWh into your house. (Yes, you can measure gas in KWh). New forced breather systems are in the 95% efficient range. Old chimney vented ones to out at 80%ish)

Even at 17F a new heat pump moves 2.5x. Put a Btu in, move 2.5 Btu into your house. Put a KWh in, move 2.5 into your house.

At 40F heat pumps move 4.5 units of heat for every 1 consumed—a huge reduction in energy use versus burning fuel

Help me out: how efficient is electric generation from gas? A Combined cycle gas plant is c. 50% efficient?

let’s call transmission & Distribution losses at 10%?

so
Burn gas, get .5 BTU of electricity
Transmit it, get .45 BTU delivered
Heat pump it at 17F, get 2.5 x .45 = 1.12 BTUs into your house, a net reduction of 10% (or close to 30% vs the typical 80% efficient home boiler)

then consider that heat pumps can use new solar and Cape Wind andit really is a net energy and cost win
 

WormtownNative

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Only problem is that heat pumps become less efficient the colder it gets (most stop working around 0 degrees F or a little below that, but are horribly inefficient at that point), so until that gets fixed, there's going to be a need for another heating system - whether it be NG, Propane, Oil, or another source. Heat pumps are just going to reduce the load on our natural gas system - while increasing our reliance on our electrical grid.

Now let me be clear, I'm not trying to be a negative jerk here - if I had the money, I'd have mini-splits in my house yesterday! But as they are currently designed, we are going to need some sort of a standby for the really cold days.
 

jklo

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then consider that heat pumps can use new solar and Cape Wind andit really is a net energy and cost win
That's why they are pushing it - because you could use alternative energy sources to generate electricity. But your numbers on what you would need is way off... burning directly is way more efficient, not to mention way cheaper.

It'd be a massive amount of additional capacity needed just from heat if Pols were to say ban FF from being used... and we def don't have that.

Only problem is that heat pumps become less efficient the colder it gets (most stop working around 0 degrees F or a little below that, but are horribly inefficient at that point)
You could use ground-source pumps which reduce the temperature where the CoP dives but they are of course way more expensive and I'm not sure if they are practical for anything other than an SFH.
 

Justbuildit

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Strange, just came across this article this afternoon. Not sure the price differential or broad availability, but it looks like there’s real progress on cold-tolerant heat pumps.

 

Arlington

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@jklo can you actually supply better numbers ? I don’t think it is useful to simply suggest better numbers exist. Ideally you’ll say both why I am wrong and by how much.

i continue to be struck by 2 facts:

1) most gas (or oil) systems 80% efficient. Getting to 90% (by replacing a boiler) is expensive for only a small reduction in gas use. And can never exceed about 98% efficiency

2) Heat pumps are natively 250% to 450% efficient (CoP of 2.5 at 17F and 4.5 at 40F). That’s a huge advantage that’s hard to squander (given inefficient gas to electric to transmission) and easy to leverage (with wind, solar, and hydro)
 

Arlington

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TLDR; Johnson Contols, Carrier and others are testing units that operate effectively down to -23F (-30C) and hope to have them in the market by 2024.

So fossil direct-burn has reached its limits, but electric tech shows it is still early on its mass adoption/ tech improvement curve

 

Arlington

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This source says transmission-distribution losses are 8% to 15% so my estimate of 10% loss seems not way off.


This suggests combined cycle gas turbine world record is 63% efficient, so my estimate of 50% seems reasonable:


Was there a point of losses I overlooked? Making electric with gas seems “efficient enough” that it doesn’t stop heat pumps from being a net reduction in gas use every time They replace a Btu of gas (and we do even better any time electric is less than 100% generated by gas units…I believe the winter grid in MA is something like 70% gas?)
 
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jklo

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@jklo can you actually supply better numbers ? I don’t think it is useful to simply suggest better numbers exist. Ideally you’ll say both why I am wrong and by how much.
I was more looking at the cost factor, but this one mini split was rated about 6.4k BTUs per kW at 17 F. A therm is about 100k. That is if I did the math right. At 40 F it could do about 11k.
 

Arlington

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I have been using the coefficient of performance (CoP) which does the (heat moved/energy used) math for me at various temps. 2.5 is typical at 17F and 4.5 is typical in whichever temp they use for “the forties” (for a new heat pump with a SEER in the 20+ range)

SEER is similar to CoP except instead of KW/KW it is in BTU/KWh
 

jklo

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I should add that I don't think we have the distribution and transmission capacity either. So you would have to greatly improve The Grid as well.

I think what would likely happen is people would just have to be in the cold.
 

tysmith95

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TLDR; Johnson Contols, Carrier and others are testing units that operate effectively down to -23F (-30C) and hope to have them in the market by 2024.

So fossil direct-burn has reached its limits, but electric tech shows it is still early on its mass adoption/ tech improvement curve
Mitsubishi already has a similar system on the market. Hopefully some competition will bring the price of it down though.
 

as02143

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I have been hearing that there's some momentum in Massachusetts for neighborhood or block by block installations of ground source heat pumps. Since a ground source well is a fairly capital intensive installation, spreading the capital and maintenance cost over several properties seems like a good use of funds. That seems do able for new build for a small infill development but I'm struggling to imagine a rehab with this model, maybe, for a small 6 to 10 unit apartment building?
 

jklo

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That seems do able for new build for a small infill development but I'm struggling to imagine a rehab with this model, maybe, for a small 6 to 10 unit apartment building?
That's going to be tough. I think you would only be talking units with electric baseboard only currently... and even then, you know how LLs are, they aren't going to be interested in blowing 20+ grand on something tenants pay.
 

as02143

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That's going to be tough. I think you would only be talking units with electric baseboard only currently... and even then, you know how LLs are, they aren't going to be interested in blowing 20+ grand on something tenants pay.
Though, now that I think about it, condos I could see - if the cost of the heating is transferred from individual condominium to the HOA/association as fees. Though, yeah, even having a tough time imagining how one induces a relatively capital-averse landlord to shell out. Would it only be electric baseboard, i presume that one could do any kind of baseboard heating.
 

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